Ball valves have been used for many years to control the flow of fluids. In its simplest from, a ball valve includes a valve body with a fluid passageway therethrough. A rotatable sphere or spheric segment, "ball", with its own fluid conduit is sealingly received in a mating "socket" in the valve body. The rotatable sphere is positioned within the valve body in the fluid passageway. When the conduit in the ball is aligned with the fluid passageway through the valve body, fluid may flow through the valve. If the ball is rotated such that the ball conduit is out of alignment with the valve body passageway, then the flow is restricted. The "off" position usually corresponds to a position of the ball wherein the conduit is at right angles to the valve body passageway. Lesser angular displacements may result in an "off" condition, however, depending upon the geometry of the valve components. The "fully on" position is typified by the ball conduit being coaxially aligned with the fluid passageway of the valve body. A ball valve can provide varying degrees of flow restriction based upon the degree of alignment of the ball conduit with the valve body passageway. Thus, for a given pressure, flow can be controlled by varying the effective orifice resulting from the degree of alignment of the ball conduit with the valve body passageway. The purpose of a fluid control valve is therefore twofold, viz., to turn the flow on and off and also to provide a desired flow rate through the valve at any given pressure.
A ball valve is usually actuated through a stem which passes through the valve body and attaches to the ball. A handle or some other means turning the stern, such as a gear, may be provided on the other end of the stem. The amount of fluid passing through the ball valve changes as the valve is actuated, for example, opened or closed. The rate of change of the flow depends upon two factors, viz., the rate of rotation of the stem and the area of alignment of the ball passageway with the valve body passageway. The area exposed is intrinsic to the valve, based upon its geometry. A particular angular orientation of the ball corresponds to a particular degree of conduit/passageway alignment and flow rate. Conventional ball valves have a rate of alignment characteristic of a pair of cylindrical conduits, one of which (ball conduit) is rotated into coaxial alignment with the other (valve body passageway).
In certain fluid control applications, however, it would be desirable to have a different rate of flow change than that provided by the conventional ball valve. e.g., for the transition from one flow rate to a greater or lesser rate to be as quick as possible. In other instances, a modest change in flow associated with a given angular displacement of the ball is desirable. It would also be desirable to have a valve that controlled the rate of flow therethrough as a linear function of ball orientation such that a change in ball orientation of a number of degrees would result in a predictable change in flow. This linear relationship would be particularly useful in automatically controlled valves wherein a digital controller or computer determines the position of the valve in response to systems demands, e.g., in an automated chemical processing operation. None of the foregoing desirable attributes are associated with common cylindrical conduit ball valves.
In certain applications, a given fluid system has multiple uses, e.g., a system that is used to fill containers with different fluids, different fluid viscosities and/or filling different sized and/or shaped containers with the same fluid. Accordingly, in those systems with varying fluid dynamic requirements relating to flow change, it is desirable to have a control valve which is adaptable to the various requirements without need for changing valves or for redirecting fluid flow through a different valve.
Similarly, there are circumstances when a fluid system with a given flow capacity, e.g., based upon pipe size and valve size would preferably be adapted to produce a lesser flow and then be readaptable to return to the original flow rate as determined by the hydrodynamic capacity of the pipeline. Furthermore, a fluid system with reduced flow would preferably have a controlled flow rate of change.
It is therefore an object of the present invention to provide a ball valve with a desired angular displacement/flow volume relationship, e.g., an approximately linear relationship, wherein a given number of degrees of ball valve movement corresponds with a given flow volume increase/decrease. It is a further object to provide such a ball valve without substantially sacrificing maximum flow volume, a ball valve which is capable of providing more than one flow change dynamic and a ball valve which can be used to selectively control overall system flow capacity while simultaneously providing control over flow rate change dynamics.